The invention relates to an ignition electrode arrangement for an internal combustion engine and to a related method.
In an internal combustion engine with spark ignition, use is normally made of an ignition electrode arrangement in which a positive electrode and an earth electrode are assembled in a sparking plug which is mounted removably in the cylinder head of the engine and has a fixed spark gap.
In order to achieve better combustion conditions in the case of inter alia low load, it is desirable to be able to use a larger spark gap than a conventional sparking plug allows, and the use has therefore been proposed of an electrode arrangement in which the sparking plug has only a positive electrode and the earth electrode is arranged on the piston of the cylinder. By selecting a suitable ignition time, it is in this way possible to obtain the desired electrode distance. However, a disadvantage is that, with a large spark gap, it is not always possible to produce a satisfactory spark because, for practical reasons, the ignition voltage has to be limited and is therefore not always adequate. In this connection, there is a risk that the spark will, instead of striking the piston, strike the cylinder head close to the sparking plug, with various disadvantages as a consequence.
In order to achieve a larger spark gap than with a conventional sparking plug, positioning a fixed earth electrode on the cylinder head has also been tried instead of having an earth electrode on the sparking plug. However, this solution does not allow the size of the spark gap to be changed, which is possible when the earth electrode is positioned on the piston.
One object of the invention is to produce an improved ignition electrode arrangement. Another object is to make possible improved spark control and in this way improved combustion control. A further object is to bring about a variable spark position.
These objects are achieved by means of an ignition electrode arrangement having the features herein disclosed and by a method having the features herein disclosed.
By making both the electrodes movable, a possibility is afforded for changing the size and/or the position of the spark gap. By furthermore controlling the size of the spark gap as a function of the current operating situation, it is possible to produce an optimum ignition spark for the current operating situation, which in turn results in advantages with regard to the possibility of, in combination with other combustion-related parameters, such as, for example, ignition time, type of fuel/air mixture, the turbulence configuration in the cylinder, temperature, degree of supercharging, compression etc., refining the combustion process in order to achieve advantages with regard to the environment, fuel consumption, drivability in different situations etc.
Further advantages and features of the invention emerge from the description and patent claims below.
The invention is explained in greater detail below by means of exemplary embodiments shown in the appended drawing.